As known, bumpers and tanks disassembled from vehicles to be demolished are conferred loose and/or crushed and compressed to form parallelepiped-like “packets”, which are constrained like packaging using strapping belts and then stored outdoors, wherein during said storage the packets are thus dirtied by mud, water, sand and soil.
Furthermore it is known that disassembled bumpers and tanks still contain a plurality of ferrous metal components, steel components, cast iron components, as well as electrical cables and terminals, headlights, flat reinforcements, polystyrene, same case also applying to ducts made of various synthetic materials, such as nylon, ABS and so on and so forth, besides residues of hydrocarbons.
The recovery/recycling of polypropylene and high density polyethylene currently occurs through crushing and grinding/granulation, with possible washing step.
In a known plant, vehicle bumpers or tanks, hereinafter referred to as “the material” is initially subjected to a step of grinding in a grinder with reduction of volume and compaction, with simultaneous iron removal, forming a grain size of the ground material of about 50-80 cm. The material thus ground is then conveyed to a windmill or granulator which provides for a further breaking to a final grain size of about 10-20 mm. Then, there follows the step of suctioning for the removal of the light components, such as pieces of paper, plastic, powder and the like, before stuffing the material in silos or big bags. A plant of this type is produced, for example, by the Italian company TPA trituratori SpA in Santa Giustina in Colle (PD).
Kun Sheng Machine Co., Ltd. advertises a plant of the type in question comprising a washing step, which equally comprises an initial grinding step for the reduction of volume and compaction, with iron removal and grinding to a grain size of about 50-80 cm and subsequent grinding stage with formation of a final grain size of about 10-20 mm, also with iron removal. The plant subsequently comprises a washing vat and a drying step for the centrifugation of the vertical column type.
In the known plants, transferring the material from one processing stage to the subsequent one occurs by using driven conveyor belts, whose support structures are fixed to the floor near the structures of the grinders, windmills, washing vat and vertical centrifuge.
A characteristic of the known plants consists in a development thereof according to a straight line and in a large installation surface.
The known plants reveal various drawbacks and disadvantages due to the mode of operation and manufacture comprising the components between the operating devices which are rigidly fixed to the floor.
After the initial grinding for reducing the meterial volume and compaction, in the ground pieces of grain size of about 50-80 cm besides the iron components there are still present other ferrous, steel, cast iron, copper, brass materials, headlights glass residues, which cause considerable wear of the blades of the windmill downstream, as well as considerable wear of the grid associated to the windmill, crucial for the reduction to the final grain size of about 10-20 mm.
This considerable reduction also requires long grinding times, during which there occurs several impacts between the metal components present in the single pieces of coarse grain size up to their final grinding to the grain size of about 10-20 mm. Such frequent and repeated impacts between hard metal components, in particular the steel beads present for closing the tanks, cause quick wear and indention of the blades of the windmill thus requiring frequent and expensive sharpening or replacement of the blades. Given that the materials entering into the windmill also have strongly adherent abrasive sand sediments, also these sand sediments contribute to causing the wear of the blades of the windmill and bearings and sealing gaskets of the relative actuation shafts. The extension of the required grinding time therefore implies a corresponding increase of electrical power consumption and considerable power of the actuation motors of the windmill due to the intense grinding effort. The extended grinding time also limits the productivity of the plant.
The traversing of the washing vat occurs with the material already reduced into the final small grain size of about 10-20 mm with a high load of metal and non-metallic foreign components, also ground in the windmill.
According to the present invention, there arises the need of indicating a method and a plant capable of overcoming the drawbacks and disadvantages of the prior art, improving the quality of the product obtained with the simultaneous increase of productivity.
This task is overcome through a plant and a method having the characteristics of claims 1 and 8.
Further developments are indicated in the respective dependent claims.
The method and the plant according to the invention allow obtaining numerous and important advantages. Firstly, they allow drastically reducing the wear of the blades of the intermediate grinder and of the windmill or granulator, with ensuing reduction of the maintenance times and costs and considerable increase of the plant productivity.
According to the proposed method and plant there also increases the quality of the finished product, i.e. the degree of cleanliness of the same and the removal—from the finished product—of every type of foreign or accompanying material, such as the finest metal components and the polypropylene or polyethylene “powder” mainly formed during the grinding, wherein the obtained ground/granulated product constitutes a secondary raw material, i.e. a high quality material, without impurity, homogeneous and with high mechanical characteristics.
A further advantage lies in the drastic reduction of the surface required for the installation of the plant according to the invention, considering the same production with respect to the known plants, wherein the required surface according to the invention is reduced to about ⅛ with respect to the prior art. This advantage is also reflected on the corresponding reduction of the surface required for the shed in which the plant is installed. A further advantage of the plant according to the invention lies in the fact that it allows a simple integration for the simultaneous processing, alternatively, of other products of plastic materials, such as for example bottle-holder crates, tubs, jerry cans and so on and so forth, which are without components of foreign materials or others, such as metal components, electrical cables, rubber, nylon and the like.
Still, an advantage of the proposed plant lies in the fact that in the required limited installation surface there are also required spaces for keeping the required vehicle or “spider” for unloading the “packets” of compressed tanks and bumpers, or the loose tanks and bumpers, from the truck and the loading thereof into the grinder for volumetric reduction and reduction into the initial coarse grain size of about 50-80 cm.
According to a first teaching of the invention it is proposed to avoid a fine grinding/granulation of material having a coarse grain size of, for example 50-80 cm, which causes the known considerable wear of the blades of the windmill and the relative grid due to the numerous metal and abrasive parts present on the material of coarse grain size, and requires the aforementioned long grinding times, as well as higher power of the actuation motors of the shafts of the windmill.
Thus, according to the teaching of the invention it is proposed to both reduce the grain size of the material to be introduced into the windmill/granulator, as well as performing greater cleaning of the material, still with the aim of reducing the wear of the blades and the various components of the windmill/granulator and extending the maintenance interventions.
A further solution according to the invention consists in associating to the washing of the material in a random intermediate grain size, of for example about 30-100 mm, in the same washing vat, a step for the separation of the foreign parts according to the differences of the specific weight, preferably with an ensuing intense subsequent cleaning through a centrifuge combined with a feeding screw tilted upwards through a preliminary centrifugation action in water and subsequent drying along the remaining part of the feeding screw of said centrifuge.
A further important teaching of the invention consists in providing the washing step no longer downstream of the windmill/granulator but upstream of the windmill/granulator, hence also contributing to reducing the wear of the blades and the other components mentioned above and located in the cutting chamber of the windmill, such as bearings and sealing gaskets.
An important structural solution according to the invention, also aimed at increasing productivity, considerably reducing the maintenance and/or repair intervention times, is that of providing means for connection between the single stages or operating devices, i.e. the conveyor belts and/or feeding screw, instead of being rigidly fixed to the floor performed on the swivel wheels, so as to be quickly moveable away from said stages or operating devices and then repositionable, and this advantageously rapidly through one user.